The Grundfos CU301 is the controller for an SQE pump. This is a variable speed pump and the sensor that is faulty is in the motor. I recently heard that Grundfos was changing the programming to let the pump cycle on and off 1000 times at 15 PSI differential, to allow time for the controller to "find the signal". This apparently happens a lot, since letting it cycle 250 times was not enough. The signal travels on the power wires that go down to the motor. This signal can be lost for several reasons. The length of wire can be a problem. Improper grounding can be a problem. The Harmonics or Stray Voltage created by the variable speed controller can be the problem. Or you could be getting a disruption of the signal from a different source such as a variable speed motor in your washing machine or something else in the area.
You will continue to have problems with that type pump. I would recommend doing away with the CU301 controller and hooking it up as a standard SQ type pump. Of course you will need a larger pressure tank than the one gallon size that came with that pump, or you can use a Cycle Stop Valve and keep the small tank.
Another customer of mine had several problems with his SQE not shutting off when it should, and the pressure would just blow off the pressure relief valve. Make sure you have a pressure relief valve. After nearly 4 years of these problems he had to purchase a new Cu302 conrtroller for about 800 bucks. The tech at Grundfos told him that the pump had already lasted nearly 4 years, and didn't understand why he was unhappy. That seems to be about the average life expectancy of those type pumps, which is crappy. A good pump should last decades.